Synthesis and Electrochemical Applications of Graphite Coated Hexanary High Entropy Oxide

Abstract

The current research work was focused on the synthesis of graphite-coated high entropy oxides (HEOs/C), as promising candidates for electrocatalytic water oxidation. The selection of the high entropy materials is based on their tailorable properties as compared to binary or ternary metal oxide nanomaterials. The HEOs were synthesized by the sol-gel method. The prepared gels were sintered at 800°C for 9 hours to get single-phase HEOs. The molar ratios were selected with 35% Al metal ion, 65% of all other cationic constituents, {Abs(Cr, Cd, Fe, Mg, Mn)6S}30 4 and 5 to 20% graphite coating was achieved by ball-milling. The structural and electrochemical analysis of the prepared electrocatalysts was done by using different techniques like X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FTlR), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDX), Cyclic Voltammetry (CV), Linear Sweep Voltammetry (LSV) and Electrochemical Impedance Spectroscopy (ElS). The XRD patterns showed that the prepared HEOs/C belong to the spinel-type high entropy oxide crystal structure. The catalytic activity of synthesized materials was evaluated towards water oxidation (OER) by performing cyclic voltammetry (CV) in the presence of 1M KOH and Methanol as a facilitating agent. The three-electrode system was employed in which Ag/ AgCI as a reference, modified glassy carbon (GC) was working, and platinum wire was used as a counter electrode in voltammetric measurements. GC electrode modification with the HEOs/C was carried out by the drop-cast method. Different kinetic parameters like diffusion coefficient (DO), mass transfer coefficient (mT), and heterogeneous rate constant (kO) were determined from cyclic voltammetric data. Among all the compositions, one with a 10% graphite-coated HEO showed excellent results for electrochemical water oxidation reaction (OER). Cyclic voltammograms showed that the peak current for OER increased remarkably with methanol addition. The higher values of lp, DO and kO for OER on SH-2 HEO/C signified its higher catalytic capacity. Electrochemical studies envisioned that all the prepared HEOs/C showed promising activity and can be used as an efficient catalyst for electrochemical water oxidation.